Most research on zoonotic diseases focuses on the pathogens, their animal hosts and their potential for infecting humans. Some zoonotic pathogens feature high levels of host specificity, meaning a small number of animal species are capable of harboring the pathogen and passing it to humans. Some other zoonotic diseases – rabies for example – have lower host specificity and can infect a wide variety of animals, generally increasing the risk of human exposure.
Now, researchers at the University of Queensland and Swansea University have demonstrated that environmental factors can play a role in host specificity and the risk of outbreaks in human populations.
In a report published in the journal Trends in Parasitology, the researchers note that empirical studies rarely consider that regional observations only reflect a parasite’s “realized” host range under particular conditions. Their report provides an overview of challenges and directions in modelling host specificity under variable environmental conditions. The authors note that combining tractable modelling frameworks with multiple data sources to account for interplay between a parasite's evolutionary history, transmission mode, and environmental filters that shape host–parasite interactions could improve efforts to quantify emerging disease risk relate to climate change.
In a previous study published in Ecology Letters, the researchers found climate change could constrain or facilitate the spread of diseases such as avian malaria. For many parasites, the researchers note, host specificity is not fixed and can vary in response to environmental conditions. Using data on host associations for avian malaria parasites (Apicomplexa: Haemosporida), they developed a hierarchical model that quantifies this environmental dependency by partitioning host specificity variation into region‐ and parasite‐level effects.
Parasites such as avian malaria, the researchers note, generally are phylogenetic host specialists, infecting phylogenetically clustered subsets of available avian hosts. The researchers found though, that the magnitude of specialization varies depending on environmental conditions.
"In the past, we've primarily looked at how many different types of animal species a pathogen infects -- widely considered an indicator of its risk to shift between host species,” says Dr Nicholas Clark, from UQ's School of Veterinary Science in a university news release. "This is just one factor, and we've found that how infected animals are related is also important. Our research also shows that different environments provide new opportunities for pathogens to interact with and infect new host species. This new line of thinking, he adds, changes how we understand and respond to emerging zoonotic disease threats.
For more on zoonotic diseases, see these articles on BovineVetOnline:
Resistance Grows Among Zoonotic Pathogens